Page 10 - Дисертаця Венгринюк

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New mathematical models were developed for predicting the fracture

toughness of transmission gas pipeline steels, taking into account hydrogen

concentration and in-service material degradation. For both conditions of 17H1S steel

(as-received and long-term service-exposed), corresponding functional relationships

were proposed based on experimental data and processed using the least squares

method. The developed models incorporate the solution of hydrogen diffusion

equations under real pipeline operating conditions, enabling prediction of hydrogen

concentration distribution through the pipe wall thickness and assessment of fracture

toughness degradation under hydrogen exposure during service.

Scientific novelty of the obtained results

The study substantiates the feasibility of reducing the loading rate of highly

ductile pipeline steels below the levels recommended in standard J-integral testing

procedures as a necessary condition to enable hydrogen absorbed in the metal to

diffuse into the fracture process zone at the tip of a pre-existing fatigue crack, thereby

allowing its effect on fracture toughness to be evaluated.

A computational model for predicting the distribution of diffusively mobile

hydrogen concentration in the metal of a pipe wall has been developed using physics-
informed neural networks. The model was used to evaluate the time-dependent

evolution of hydrogen concentration distribution in the pipe wall material.
Mathematical models have been formulated for predicting the fracture

toughness of pipeline steels as a function of hydrogen concentration, accounting for
service-induced material degradation. The developed models are integrated with the

solution of the hydrogen diffusion equation for real pipeline operating conditions,

enabling prediction of the evolution of static fracture toughness of steels in gas

transmission pipelines depending on hydrogen concentration and material

degradation during service.

A criterion has been substantiated for determining the limit state of pipeline

steel in terms of static fracture toughness under hydrogen transport conditions. This

criterion is based on the established relationships describing the influence of hydrogen

charging intensity and loading rate on the fracture toughness characteristics of